Acoustic wave filter device with branched ground wiring sandwiching the IDT area

Abstract

An acoustic wave filter device has a balance-unbalance conversion function and has an increased out-of-band attenuation. The acoustic wave filter device includes a 5-IDT-type longitudinally coupled resonator-type acoustic wave filter unit including IDTs that are connected between an unbalanced terminal and first and second balanced terminals, and the IDTs and are connected to the first and second balanced terminals, respectively, that is arranged between the unbalanced terminal and the first and second balanced terminals. A second ground wiring that connects the end portions of the unbalanced-side IDT on the side connected to the ground potential to a ground terminal is separated from a first ground wiring. The second ground wiring includes first and second branched wiring portions, and the first and second branched wiring portions are arranged so as to sandwich an area in which the IDTs are provided.

1. An acoustic wave filter device including an unbalanced terminal and first and second balanced terminals and having a balance-unbalance conversion function, the acoustic wave filter device comprising:
 a piezoelectric substrate; 
 a longitudinally coupled resonator-type acoustic wave filter unit including at least three IDTs, the longitudinally coupled resonator-type acoustic wave filter unit being provided on the piezoelectric substrate and being connected between the unbalanced terminal and the first and second balanced terminals; 
 a first ground wiring provided on the piezoelectric substrate and including a first end portion and a second end portion, the first end portion of the first ground wiring being connected to a ground-side end portion of an IDT connected to the first or second balanced terminal among the at least three IDTs; 
 a second ground wiring provided on the piezoelectric substrate and including a first end portion and a second end portion, the first end portion of the second ground wiring being connected to a ground-side end portion of an IDT connected to the unbalanced terminal; and 
 first and second grounding electrode pads provided on the piezoelectric substrate, the second end portions of the first and second ground wirings being electrically connected to the first and second grounding electrode pads, respectively; wherein 
 the second ground wiring is arranged to branch to first and second branched wiring portions in a middle portion from the first end portion toward the second end portion, and the first and second branched wiring portions are arranged so as to sandwich an area in which the at least three IDTs are provided. 
 
     
     
       2. The acoustic wave filter device according to  claim 1 , wherein the first and second grounding electrode pads are defined by one electrode pad. 
     
     
       3. The acoustic wave filter device according to  claim 1 , wherein the first ground wiring includes a portion that is laminated with a portion of the first branched wiring portion with an insulating film therebetween. 
     
     
       4. The acoustic wave filter device according to  claim 1 , further comprising:
 a dielectric laminated on the piezoelectric substrate; wherein 
 the acoustic wave filter device is a boundary acoustic wave filter device in which at least three IDTs are disposed between the piezoelectric substrate and the dielectric. 
 
     
     
       5. The acoustic wave filter device according to  claim 1 , wherein the acoustic wave filter device is a surface acoustic wave filter device.